Impact modifiers are widely used to improve the impact strength for thermoplastics and thermosets with the aim to compensate their inherent brittleness or the embrittlement that occurs at ambient temperature but also and especially at sub zero temperatures, notch sensitivity and crack propagation. So an impact modified polymer is a polymeric material whose impact resistance and toughness have been increased by the incorporation of phase micro domains of a rubbery material. This is usually done due to the introduction of microscopic rubber particles into the polymer matrix that can absorb the energy of an impact or dissipate it and thereby improve the impact strength of the polymeric material. One possibility is to introduce the rubber particles in form of core-shell particles. These core-shell particles that possess very generally a rubber core and a polymeric shell, having the advantage of a proper particle size of the rubber core for effective toughening and the grafted shell in order to have the adhesion and compatibility with the thermoplastic matrix. One type of core-shell particles is acrylic core shell particles or acrylic impact modifiers (AIM).
The performance of the impact modification is a function of the particles size, especially of the rubber part of the particle, and its quantity or ratio to the shell and the thermal characteristics. There is an optimal average particle size in order to have the highest impact strength for a given quantity of added impact modifier particles.
Furthermore the thermal characteristics are important, in the case for having a rubber particle; the glass transition temperature (Tg) of the rubber has to be far below the application temperature. The Tg of the polymeric rubber particle is usually below 0° C.
An objective of the present invention is to provide a new impact modifier that performs better then the nowadays-available standard impact modifiers.
By better performance is meant that the impact modifier performs either better in terms of the impact strength used at the same quantity as the nowadays-available standard impact modifiers or the same impact strength is obtained by incorporating a less quantity of the impact modifier in comparison the nowadays-available standard impact modifiers in a thermoplastic resin, while keeping other characteristics.
Another objective of the present invention is to provide an impact modifier that has a significantly better impact performance while keeping a good compromise of processing quality once incorporated in a thermoplastic resin and an acceptable visual quality of the final part.
Still another objective is to provide an impact-modified composition that comprises at least one thermoplastic resin that has a significantly better impact performance.
Surprisingly it has been found that the use of 2-octylacrylate as monomer in the polymeric impact modifier increases significantly the impact strength of the thermoplastic resin, without loosing the other essential characteristics as processing and other characteristics and final technical performances.
The document EP1061100 discloses multilayer core-shell particles especially in the examples acrylic core shell impact modifiers having a core based on butyl acrylate and a shell based on methyl methacrylate.
The document WO2008/051443 describes impact modified polylactide resins. The impact modification and low haze is obtained by adding an acrylic core shell impact modifier in form of larger particles or agglomerates and smaller particles and agglomerates. The acrylic monomers given for the rubber phase of the impact modifier are butyl acrylate and 2-ethyl hexyl acrylate.
The document WO2009151977 discloses biodegradable impact modified polymer compositions. The compositions comprises acrylic core shell impact modifiers preferably the rubber core based on butyl acrylate, 2-ethyl hexyl acrylate and butadiene.
All prior art is completely silent about the 2-octylacrylate as acrylic monomer in an acrylic polymeric impact modifier and thermoplastic resin compositions comprising such an impact modifier.